1. Field of the Invention
The present invention concerns a temperature-dependent switch having a temperature-dependent switching mechanism; a closed housing, containing the switching mechanism, which has a lower part as well as an upper part made of insulating material; two stationary contacts provided on the upper part on its inner side, each contact being electrically connected to an external terminal associated with it; and a current transfer member, actuated by the switching mechanism and electrically connecting the two stationary contacts with one another as a function of temperature.
2. Related Prior Art
A switch of this kind is known from DE 26 44 411 C2.
The known switch has a housing with a cup-shaped lower part into which a temperature-dependent switching mechanism is placed. The lower part is closed off by an upper part which is retained on the lower part by the elevated rim thereof. The lower part can be manufactured from metal or insulating material, while the upper part is in any event manufactured from insulating material.
Resting in the upper part are two rivets whose inner heads serve as stationary contacts for the switching mechanism. The switching mechanism carries a current transfer member in the form of a contact bridge, which as a function of temperature is brought into contact with the two stationary contacts and then electrically connects them to one another.
The external heads of the two rivets serve as solder terminals for leads.
The temperature-dependent switching mechanism has, in a manner known per se, a bimetallic disk as well as a spring disk which is penetrated centeredly by a pin which carries the contact bridge. The spring disk is guided peripherally in the housing, while the bimetallic disk is braced, depending on its temperature, against the floor of the lower part or against the rim of the spring disk, and thereby either allows the contact bridge to make contact with the two stationary contacts or lifts the contact bridge away from the stationary contacts so that the electrical connection between the external terminals is interrupted.
This temperature-dependent switch is used, in known fashion, to protect electrical devices from overheating. For this purpose, the switch is connected in series with the device to be protected, and is arranged mechanically on the device so that it is thermally coupled thereto. Below the response temperature of the bimetallic disk, the contact bridge rests against the two stationary contacts, so that the circuit is closed and the device to be protected is supplied with power. If the temperature rises above an allowable value, the bimetallic disk lifts the contact bridge away from the stationary contacts, so that the switch opens and the supply of power to the device to be protected is interrupted, so that the latter can cool off again.
Although the known switch technically meets all requirements, it still has a series of disadvantages which are associated with its production and its installation on a device to be protected.
One disadvantage is the complex manufacture of the known switch: after production of the cover, the rivets must still be subsequently mounted on it. A further disadvantage lies in the fact that leads must still be soldered onto the external rivets; this cannot, as a rule, be automated. This means, however, that the production of a switch that is equipped with leads and ready to be connected is in this case time-consuming and thus cost-intensive.
Further disadvantages are to be seen in conjunction with installation of the known switch on a device to be protected. The known switch has only solder terminals or leads, while crimp or screw terminals are often required today. If the lower part is manufactured of plastic, thermal coupling to the device to be protected is relatively poor with the known switch, while with a lower part manufactured of metal, although good thermal coupling can be achieved, the elevated metal rim of the lower part must often additionally be electrically insulated from the outside.
In summary, therefore, the disadvantages of the known switch are on the one hand complexity of manufacture and on the other hand the fact that capabilities for installation on a device to be protected are insufficient for many applications.
In this connection, a temperature-dependent switch having a lower housing part made of metal and an upper housing part made of insulating material is known from DE 31 22 899 C2. Embedded into the upper part are two connector tongues, the first of which is connected to a stationary contact arranged centeredly. The second connector tongue is equipped with tabs which, when the upper part is installed, are electrically connected to the lower part.
Arranged in the interior of the closed housing constituted in this fashion is a bimetallic switching mechanism which, as a function of its temperature, creates an electrically conductive connection between the stationary contact and the lower housing part and thus between the two connector tongues.
A disadvantage of this switch is that assembly, in particular the arrangement of the upper part on the lower part, is complicated, because the tabs configured integrally with the second connector tongue must, for the purpose, be oriented appropriately. If manufacturing errors or inaccuracies are present, the reliability of the electrical connection between the connector tab and the lower part is not guaranteed.
As was already the case with the switch mentioned at the outset, here again the elevated lower part made of metal requires lateral insulation for certain applications.
A further disadvantage of the known switch lies in the fact that the connector tongues project vertically upward out of the upper part, which interferes with installation on the device to be protected and, in particular, with electrical connection.